1. Field of the Invention
The present invention relates to an ISUP (ISDN User Part) network, and more particularly to a method for testing continuity of ISUP relay call.
2. Description of the Background Art
FIG. 1 is a schematic view of an ISUP network in accordance with a conventional art.
As shown in the drawing, a preceding switching system 11 generates a continuity testing message, that is, a initial address message (IAM), and a testing sound to check continuity of a communication path, and a following switching system 12 forms a communication path loop and performs a function to request a call set-up according to the continuity checking result transmitted from the preceding switching system 11.
The method for testing continuity of an ISUP relay call in an ISUP network constructed as described above will now be explained with reference to the accompanying drawings.
In setting up a call, the preceding switching system 11 judges whether a continuity testing is to be performed for a corresponding relay line, on the basis of the usual state of relay lines.
If it is judged to need a continuity testing for a corresponding relay line, as shown in FIG. 2, the preceding switching system 11 sets the value of a connection characteristic indicating parameter of the initial address message (IAM) (that is, a call set-up message), that is, it sets a continuity testing indicating field as a continuity testing required value, and transmits the IAM to the following switching system 12.
Upon receiving the IAM from the preceding switching system 11, the following switching system 12 forms a communication path loop 12-1 to perform a continuity testing.
After a predetermined time elapses, that is, after a sufficient time during which the following switching system 12 sets a communication path loop 12-1 upon receipt of the IAM elapses, the preceding switching system 11 transmits the testing sound generated by a sound source. When the testing sound is completely transmitted, the preceding switching system stops transmitting the testing sound.
Subsequently, the preceding switching system 11 measures a reflected sound returned through the communication path to check the state of the communication path, and transmits a continuity (COT) message carrying the communication path checking result to the following switching system 12.
Then, the following switching center 12 releases the communication path loop 12-1 and then continues or discontinues a call according to the COT message transmitted from the preceding switching system 11.
In other words, in case that the communication path is in a good condition, the following switching system 12 requests a call set-up, whereas, in case that the communication path is in a bad condition, the following switching system 12 transmits a release (REL) message to the preceding switching system and releases a call.
As described above, in the method for testing continuity for an ISUP relay call in accordance with the conventional art, the testing sound transmission and the continuity testing of the communication path are all performed by the preceding switching system.
However, the preceding switching system transmits the testing sound to the following switching system after a predetermined time sufficient for setting up a communication path loop elapses after the following switching system receives the IAM. Thus, the preceding switching system waits for a considerably long time to transmits a testing sound, resulting in that a long time is consumed to set up a call.
In addition, since the following switching system does not set up a call until it receives the continuity result message (COT) from the preceding switching system, call set-up delay occurs in the following switching system.
Moreover, since the preceding switching system should transmit the message indicating continuity testing to the following switching system, an additional load factor is caused in the preceding switching system.
Therefore, an object of the present invention is to provide a method for testing continuity of an ISUP relay call which is capable of reducing a load in a preceding switching system and shortening time for setting up a call in a following switching system by performing testing sound transmission and continuity testing in the following switching system.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for testing continuity of an ISUP relay call, in which, in setting up a call, a preceding switching system transmits a call set-up message, that is, an initial address message (IAM), for continuity testing to a following switching system and at the same time forms a communication path loop, and upon receipt of the IAM, the following switching system transmits a testing sound to the communication loop to test continuity of the communication path.
To achieve the above objects, there is also provided a method for testing continuity of an ISUP relay call, including the steps of: receiving a call set-up message (IAM) from a preceding switching system; identifying the received IAM to judge whether a continuity testing is to be performed; generating and transmitting a testing sound to a communication path loop in case that a continuity testing is to be performed upon judgement; and identifying the state of the communication path on the basis of the testing sound reflected from the communication path loop and controlling setting up of a call.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.